1 Notes on Linux SCSI Generic (sg) driver
2 ---------------------------------------
3 20020126
4Introduction
5============
6The SCSI Generic driver (sg) is one of the four "high level" SCSI device
7drivers along with sd, st and sr (disk, tape and CDROM respectively). Sg
8is more generalized (but lower level) than its siblings and tends to be
9used on SCSI devices that don't fit into the already serviced categories.
10Thus sg is used for scanners, CD writers and reading audio CDs digitally
11amongst other things.
1213Rather than document the driver's interface here, version information
14is provided plus pointers (i.e. URLs) where to find documentation
15and examples.
161718Major versions of the sg driver
19===============================
20There are three major versions of sg found in the linux kernel (lk):
21 - sg version 1 (original) from 1992 to early 1999 (lk 2.2.5) .
22 It is based in the sg_header interface structure.
23 - sg version 2 from lk 2.2.6 in the 2.2 series. It is based on
24 an extended version of the sg_header interface structure.
25 - sg version 3 found in the lk 2.4 series (and the lk 2.5 series).
26 It adds the sg_io_hdr interface structure.
272829Sg driver documentation
30=======================
31The most recent documentation of the sg driver is kept at the Linux
32Documentation Project's (LDP) site:
33http://www.tldp.org/HOWTO/SCSI-Generic-HOWTO34This describes the sg version 3 driver found in the lk 2.4 series.
35The LDP renders documents in single and multiple page HTML, postscript
36and pdf. This document can also be found at:
37http://sg.danny.cz/sg/p/sg_v3_ho.html3839Documentation for the version 2 sg driver found in the lk 2.2 series can
40be found at http://sg.danny.cz/sg/. A larger version
41is at: http://sg.danny.cz/sg/p/scsi-generic_long.txt.4243The original documentation for the sg driver (prior to lk 2.2.6) can be
44found at http://www.torque.net/sg/p/original/SCSI-Programming-HOWTO.txt45and in the LDP archives.
4647A changelog with brief notes can be found in the
48/usr/src/linux/include/scsi/sg.h file. Note that the glibc maintainers copy
49and edit this file (removing its changelog for example) before placing it
50in /usr/include/scsi/sg.h . Driver debugging information and other notes
51can be found at the top of the /usr/src/linux/drivers/scsi/sg.c file.
5253A more general description of the Linux SCSI subsystem of which sg is a
54part can be found at http://www.tldp.org/HOWTO/SCSI-2.4-HOWTO .
555657Example code and utilities
58==========================
59There are two packages of sg utilities:
60 - sg3_utils for the sg version 3 driver found in lk 2.4
61 - sg_utils for the sg version 2 (and original) driver found in lk 2.2
62 and earlier
63Both packages will work in the lk 2.4 series however sg3_utils offers more
64capabilities. They can be found at: http://sg.danny.cz/sg/sg3_utils.html and
65freecode.com
6667Another approach is to look at the applications that use the sg driver.
68These include cdrecord, cdparanoia, SANE and cdrdao.
697071Mapping of Linux kernel versions to sg driver versions
72======================================================
73Here is a list of linux kernels in the 2.4 series that had new version
74of the sg driver:
75 lk 2.4.0 : sg version 3.1.17
76 lk 2.4.7 : sg version 3.1.19
77 lk 2.4.10 : sg version 3.1.20 **
78 lk 2.4.17 : sg version 3.1.22
7980** There were 3 changes to sg version 3.1.20 by third parties in the
81 next six linux kernel versions.
8283For reference here is a list of linux kernels in the 2.2 series that had
84new version of the sg driver:
85 lk 2.2.0 : original sg version [with no version number]
86 lk 2.2.6 : sg version 2.1.31
87 lk 2.2.8 : sg version 2.1.32
88 lk 2.2.10 : sg version 2.1.34 [SG_GET_VERSION_NUM ioctl first appeared]
89 lk 2.2.14 : sg version 2.1.36
90 lk 2.2.16 : sg version 2.1.38
91 lk 2.2.17 : sg version 2.1.39
92 lk 2.2.20 : sg version 2.1.40
9394The lk 2.5 development series has recently commenced and it currently
95contains sg version 3.5.23 which is functionally equivalent to sg
96version 3.1.22 found in lk 2.4.17 .
979899Douglas Gilbert
10026th January 2002
101dgilbert@interlog.com